In armature winding machines, the wire being wound in the slots of the armature is cut at the hook on the commutator. The cutting step is carried out normally by means of pulling the wire cut it on the sharp profile of the hook. This way ends of wire are prevented from extending beyond the hook.
Furthermore, in the change from an armature already wound to the following unwound armature, the terminal portion of the wire has to be temporarily gripped so that it is available to the flier for the next hooking step.
Both for cutting the wire and for maintaining it temporarily a collet/cutter can be used as in U.S. Pat. No. 4,826,092 or, alternatively, a “gripper” tool, as in EP0989659.
The gripper consists in a movable arm having at the end an holding element. Normally two gripper tools are provided for each armature to be wound, one for each flier. An upper gripper is arranged above the commutator and a lower gripper under the commutator, both laying in the winding machine vertical plane of symmetry, that at the two fliers at opposite sides.
Typical steps for each gripper tool for gripping temporarily the wire and cutting it on the hook of the commutator are the following:                at the end of a winding step on an armature the support of the gripper moves forward and the gripper approaches the commutator clamping the stretched wire that extends from the flier to the commutator;        the wire is wound about the hook creating an α-shaped loop;        the gripper carries out then a quick and brief backward movement from the hook so that the wire is cut; the cut wire end is therefore close to the hook of the wound armature;        the gripper moves away, whereby on it the other cut end of the wire is present, that comes from the flier; the wound armature is carried away and a new armature to be wound is automatically presented;        the gripper is lowered again and the wire is wound about a hook of the new armature creating another α-shaped loop;        the armature effects then a quick and brief movement of rotation, and owing to a relative movement between gripper and armature the wire is pulled against a sharp edge of the hook that causes a further cut, so that an end belongs to the segment of wire already present on the gripper and the other end is wound on the hook and belongs to the wire coming from the flier;        the gripper moves back to a stand-by position and releases the segment that falls, while the winding starts again;        at the end of winding the above steps are repeated.        
The cycle exemplified above is that normally used in a winding machine of two poles armatures; similar cycles are possible for winding armatures with more poles.
The step of releasing the wire segment that falls thus in a container located beneath is somewhat different for the upper gripper. In fact, the upper gripper carries out in some way a movement of deviating from the vertical of the commutator before releasing the segment. The lower gripper, instead, is in a more favourite position, because it has not devices that block the fall of the segment, and it has not to deviate.
The grippers according to the prior art are normally hinged to a support in order to carry out the movements of approach/withdrawal from the winding zone by means of a rotation about a pin by means of a pneumatic actuator.
The problems that arise with the existing grippers are the following:                the approach and withdrawal movements of the gripper with respect to the commutator even if quick, are not enough precise for allowing a control of the stroke;        without control it is not possible to adjust the movement of the gripper according to the cross section of the wire, the shape of the hook, the diameter of the commutator, since the pneumatic drive does not allow this flexibility;        at the moment of the cut the wire must have a trajectory at most limited, in order to remain as far as possible within the hook and without interfering with the end of the wire already present;        the movement of withdrawal of the gripper from the commutator provides a rotation in the vertical plane that causes the gripper to follow a circular trajectory, and this causes a variation of angle of the stretched wire from the commutator to the gripper, with the consequence that the wire has a brief diversion on the hook before cutting, thus spoiling the end of the wire previously cut.        
Furthermore, whereas below the lower gripper there are not further elements that block the fall of the segment, the upper gripper must bring the segment far from the vertical of the commutator before releasing it. In this case:                the withdrawal of the upper gripper for releasing the segment has to be fact in order to not obstruct the flier while winding;        the segment of wire has to be released safely, to avoid that remains on the gripper and spoils the next hooking step.        